Field of the Invention
The invention relates to a pressurizer with a casing, in which at least one spray line ends.
Such pressurizer are customary in a nuclear power plant with a pressurized water reactor. There, they are connected to a branch of a primary circuit which leads from a reactor. In the pressurizer, there is a spray system which is fed with water from a primary-circuit line that leads from a steam generator to the reactor. The water which is introduced through the spray system is therefore relatively cold as compared to the water which is situated inside the pressurizer. The spray system is generally closed off through the use of spray valves. The spray valves are only opened when an excessively high pressure is generated in the pressurizer, and the pressure in the pressurizer is lowered by praying-in relatively cold water. However, a valve cone of one of the spray valves may also have a small hole, so that some water is sprayed into the pressurizer continuously, even when the spray valve is closed.
Heretofore, it has been customary to guide the spray lines into the interior of the pressurizer through a so-called spray lid, which is screwed onto a central flange on an upper dome of the pressurizer. To that end, the spray lines initially run upward from the primary circuit and then, after they have passed through a bend above the pressurizer, they run downward into the pressurizer.
Heretofore, a so-called spray shroud has been necessary to ensure that the relatively cold water which is sprayed-in does not strike the hot wall of the pressurizer, which would lead to undesirable transient temperatures that would cause material fatigue. That spray shroud is a sheet-metal cylinder which is open at the top and bottom and is disposed concentrically inside the pressurizer. The water which is sprayed-in then strikes the inner wall surface of the sheet-metal cylinder, without coming into contact with the pressure-supporting casing wall.
Spray lines are made from austenitic steel. Due to their small diameter, it is not possible for weld seams to be ground internally. Consequently, it is not possible to completely rule out fracture of a spray line. If a spray line breaks, expensive measures are needed to ensure that line parts which are thrust outward or an emerging jet of steam do not cause secondary damage in the power plant.
Since the spray lines are guided downward into the pressurizer, at least the downwardly directed part of the spray lines empties when the spray valves are closed. Then, saturated steam from the pressurizer can penetrate into the spray lines and condense therein. The condensate then flows back into the pressurizer and makes room for fresh saturated steam. Therefore, according to the principle of conventional steam heating, at least the downwardly directed section of a spray line is continuously heated. Then, due to the temperature differences, feeding relatively cold water in when necessary may lead to material fatigue of the spray lines. If the spray valves are disposed above the pressurizer, the saturated steam also reaches the spray valves, where it can cause damage in the same way. Since the saturated steam inside the pressurizer is radioactive, there is also a risk of the spray lines as well as the spray valves being exposed to radiation.